Vacuum transfer and placement mechanisms are well known in the electronic assembly art and are used for retrieving electronic components, such as connectors, from a supply source and transferring them by applying negative air pressure to the connectors and placing them onto a printed circuit board in preselected positions for soldering. Typically, such mechanisms are used with robotic assemblers and include a transfer arm with an engagement end that is pneumatically connected to a source of negative air pressure. This negative air pressure creates a vacuum at a vacuumsuction nozzle at the engagement end of the transfer arm which can be used to effectively "grab" a connector so that the connector may be robotically transferred into a placement position with great accuracy onto a circuit board or like component.
With the ever-increasing miniaturization of electronic circuits and components, it often is difficult to provide a surface area of a size sufficient for engagement by a vacuum-suction nozzle. In fact, most electrical connectors, particularly electronic connectors for mounting on a printed circuit board, are devoid of large flat portions which can be engaged by the vacuum-suction nozzle. For instance, one type of connector adapted for mounting on a circuit board includes a plurality of terminals arranged side-by-side in a generally parallel array, with each terminal having an inclined cantilever-like spring contact arm extending upwardly and having a contact portion projecting above the top surface of the connector housing. The cantilevered spring contact arms are inclined in opposite directions alternatingly lengthwise of the connector to provide balanced forces when the contact portions of the arms are engaged by a complementary mating connector, a second A printed board or the like. By alternating the terminals, there is no room whatsoever for a flat surface area engageable by a vacuum-suction nozzle.
One solution to the above problem would be to simply enlarge the connector to provide an adequate surface area for the vacuum-suction nozzle to engage. This solution is unacceptable because the enlarged connector would take up too much valuable "real estate" on the printed circuit board. Another solution to the problem would be to eliminate the alternating arrangement of the terminals and have all of the terminals with their cantilevered spring contact arms being oriented in only one direction, leaving sufficient area behind the cantilevered arms for engagement by the vacuumsuction nozzle. This solution in unacceptable because the mating forces on all of the spring contact arms oriented in only one direction will create undesirable stresses concentrated at one lateral side of the connector. Such undue stresses could actually destroy the solder connections of the terminals to the circuit traces on the printed circuit board. The present invention is directed to solving these problems by uniquely arranging the terminals in groupings which allow for a sufficient surface area on the housing for engagement by the vacuum-suction nozzle, while avoiding concentration of mating stresses to one side of the connector.